Studies of the extracellular matrix over the track upon which the LHRH cells migrate from the olfactory placode to the CNS have shown that the appearance of N-CAM directly correlates with the appearance of LHRH cells, whereas fibronectin does not. LHRH cells are present in tissue cultures derived from embryonic nasal regions of mice. A transgenic line was established using a human LHRH promoter joined to the SV40 t-antigen construct. These animals show abnormal reproductive function and on examination very few LHRH immunopositive cells were detected in the forebrain. Transgenic mice containing constructs which have both AVP and OT genes together exhibit cell-specific expression, whereas transgenic mice with only one of these genes exhibit only ectopic expression. Studies of aldose reductase mRNA in lens and kidney show that expression of this gene is inhibited by galactosemia and hyperglycemia. Rat brain slice-explant cultures have been used to show that estrogen and inhibition of spontaneous electrical activity by TTX leads to inhibition of LHRH gene expression. Exaggerated coexistence of CGRP and substance P peptides in postnatal sensory neurons in vitro was found.